Manufacture of cement



Dec. 25, 1934. v E, J MAUs-r 1,985,868

' MANUFACTURE OF CEMENT Filed Oct. 21, 1931 3 Sheets-Sheet 1 WA TE}? WA75/? MA TE R/A LS M/XERS 43 EQUA LIZ/N6 STORA GE INVENTOR (ERNEST J.MAUST- ATTORNEY E. J. MAUST I 1,985,868

MANUFACTURE OF CEMENT- Fil ed Oct. 21. 1951 3 Sheets-Sheet 2 SHALE LIMESTONE FIG. 2.

LOW LIME HIGH LIME TH/CKENER TH/CKENER a 99 M00 10/ r402 SMALL FILL ANDDRAW CORRECT/ON TANKS EQUAL/Z/NG T //09 STORAGE TANK/ INVENTOR, ERNESTJ. MAUST'.

De1:.25,1934. y MAU T 1,985,868

MANUFACTURE OF CEMENT- Filed Oct. 21, 1931 1 3 SheetsSheet 3 LOW LIME aHIGH LIME THICKENER 75 TH/CKENER OVERFLOW FROM BOWL CLASS/PIERMED/UML/ME HIGH um: TH/CKLNER TH/CKENER TH/C/(ENER INVVENTOR RNST J.MAusr. BY

ATTORNEY PatentedDec. 25, 1934 I w;

. i Ac'rUREoF CEMENT i Ernest J. Maust, NewYork,.N. Y., assignorto V l,.Dorr c pany, Inc.,' New ration "of Delaware Application ctober 121;1531, Serial No I s-cl ims; (o l f dPzsi The present inventionrelates tothe manufac tureof Portland cement, with special reference to a methodofzand apparatus for controlling the composition of the mixture of rawconstituents '5 as prepared by what is knownkas'the wet process;

I Since the raw materials used in the manufacture of cement, such "aslimestone and shale, are obtained from quarriesornatural deposits, thereis usually a considerable variation in :chemical composition ofmaterials .robtained from different areas or'differentstrata of: thequarry, and whilepreliminary chemical control may therefore be efiectedin a general waybyselective quarrying, such controlis at most a veryrough approximation and must .be followed by suitable correction atanother step or steps in the process. 1Heretofore thefnecessarycorrection has been made by running the ground 7 mixture from{ the millsinto batch slurry mixers or correctiontanks from which catch samplesaretaken and analyzed' Two or more such tanks thusvfilled and tested, aremaintained with high lime and low lime mixtures which are drawn.oiiinsuitable proportions into .kiln feedbasins to'iform theproperi mixfor burning. Such correction tanks' require fromrsix to eight hoursfilling time; which together with thetime required ,for sampling and:analyzing results in a lapse of ten or 'twelve' hours from the time theraw materials for that batch'entered the mills, with the disadvantagethat such analysis lags much too farbehindthe mill feed topermit of anybut a very general, control by variation ofjthecomposition of; millfeed; 7 I I 1 I i The chief object :of the present invention is toobviate this ,disadvantage'an'd provide a substantially continuous andmore accurate .contr'olof the composition of the mixture-throughout theprocess. 'I'his object is accomplished through the uti-i lization ofclosed circuit grinding with repeated analysis of the mill; output atrelativelyshort pe-,

riods, two hours orleSSf, While repeatedly correct" ing the milli feedtoi compensate for, variations from the desired" mixture as indicated bysuch analyses and thus cause the composition of the mill outputtoaverage that desired together with the use of a thickener in amannerto receive and continuously blend the 1 fluctuations I incomposi-; tion of the milloutput wherebyeven relatively widefluctuations if of :suflicientlyj short duration and properly average or"compensated, I will be smoothedout in thegthickener underflowp Furthercorrection of the thickener underflow is ob tained through the practiceof what may be termed closed circuit thickening, which comprisesrecirculating a portion of the underfiow through the;thickener,advantage being taken of the variation 0f mixt'ure withindififerent' parts of the thickener by recirculating a'porti'on of theunderflow via a zone in the'thickener containing a mixturerich in-theconstituent needed forl correctfion. The amount of variation necessaryfor correction is slight because variationsin the thickener underfiowtake the form of a relatively slow trend in which the timerequired foravariation sufficient to necessitate correction is inclusive of a periodI sufiicient :for the 1 making of several analyses'of the underfiow.

-A' modification of the invention accomplishes this object of continuousand accurate control, through the use of closedcircuit grinding incombinationwith a plurality of 'thic'keners arrangedv to-coofier'atewith each other in the correction of fluctuations in" compositiorf-oi:the 1 mill 1 output. To this end variations of mixtures discharged fromthe grinding circuit'rich in lim'eare blended or averaged separatelyfromthe variations of mixtures deficient in'lime,*in high and low limethickeners, respectively,and final adjustment effectedby proportionateblending of the underflow from the difierent thickeners according to theanalyses ofsuchun'derfiows; There may be several high-lime and severallow-lime thickeners toiprovide a number of grades of each of thetwokinds of mixtures for final adjustment. There may also be one forrnioremedium 'thickeners for receiving substantially correct: or mediummixture, or for receivingmutually compensating fluc- V tuations inImixture of'such'short duration: as to readily blend into an averagewhich will equalorsapproximate the desired composition.

"In distributing the mill output to the difierent thickeners itmaybediverte'd substantially all to one thickener :at a. time, I or splitamong two or more thickeners in portions difiering according to the kindof mixture being delivered at the time and the difference in kind ofaverage mixture to be stored in each of such thickeners. I

i For final correction of the slurry to bring it to the'proper complexratios'and fine adjustment of lime ratio before going to the filter orkiln, it is passed through a plurality of correction tanks connected inseries and supplied with t the slurry and the necessary correctionmaterials in a manner' enabling the: slurry to be detained and sampled,and'further corrected if necessary, at successive points en route to thefilter or kiln without interruption to continuity of supply to thefilter or kiln. I I I i Other objects and advantages of the inventionwill be apparent froma perusal of the following lime and low limethickeners.

Fig. 4 is a fiow sheet showingthe'method of proportioning thethickenerfeed amdng'high lime, low lime and medium mixture thickeners.

Referring to the drawings in detail, and first to Fig. 1, bins 1 and 2are for storing the main raw material such as crushed cement rock orlimestoneior. ready, supply toa primary or coarse grindingball mill 3;as indicated by the flow line 4:2. The rock; roughly classified, isstored, inthe binsl and-=21 as highlime; and low lime rock, re:spectively, suitable feedcontrol means -such as the.- usual variablespeed feeders, indicated at 5 and; 6, being. operatively connected;between each biniand. the: mill. for. proportioning the materials fed tothe mill. @The primary {mill 3 is arranged, inplosed circuit'with.-a=.Dorr classifier 7, from which theoverflow is :fed intothe bowl8 of a Dorr bowl classifier 9 as indicatedbytheflow line 10. Suitablemeans are provided for adding water to th'e mill and cIaSsifierasindicated at 11 and 12. to maintain optimum= working dilutions. Wherethe-raw material taken from the. bins, 1 and 2 contains. a' considerablequantityzof natural fines, it may be. introduced directly into theprimary classifier 7, the raw materialjbeing supplied in;a sizesufficiently small-for :such method of .feed; The bowkclassifier 9.is-arrangedin closed circuit with a. secondary, orrfine grinding milll3,means being provided. forjadding. water to the bowl, 8

of; the classifier and to mill 13.asindicatedat' Hand 15, and ior addingclay or clay slipto the secondary. mill Bras. indicatedrat; 16. r

est dilution and. in a turbulent and well dispersed;

condition; :w I

The. thickener-.17 is. a Dorr. type' traction thickener of relativelylarge capacity in proportion to the. grinding apparatusitoj aiiorldawide margin. of storage capacity. .It hasthe usual slopingbottom 22along :whichthe thickened. slurryis raked by the usual rotating rakearms231and' 24' toward the :central 1 discharge. point. 25 to; the:underflow line 26.: It is also provided with the *usual central,annular, feed trough-27: which receives the feed from the-bowl 8 .asindicated bythe flow line'18.

and delivers it'intd. the thickener'below'theliquid level 128,)all as'is-Jwell understood in' the' art. The thickener overflow 29 may lead te-waste or be pas'sed' back into circuit in the usual manner asiwatersupply tothe grinders' or classifiers. "A

-,-, Underfiow from the thickener is conducted by way of pump 37 to asurge tank 38 as indicated by flow line 39, the surge tank 38discharging through flow line 40 and valves 41 and 42 into two or moreslurry mixers 43 and 44, the slurry mixers in turn being arranged todischarge through regulating valves 45 and 46 into an equalizing storagetank 47. From the storage tank the slurry passes on to the usual kilnsor other suitable burning means as indicated at 48, either directly orthrough filters. The surge tank .38

is arranged to discharge also into the returnv feed launder 30 asindicated by flow line 49. Suit.- able valve means 50 and 51 areprovided in the flow lines 40 and 49, respectively. A sampler 52,preferably of the automatic type, is arrangedto take samples of the flowthrough flow line 40;

The apparatus is also arranged to facilitate the taking of samples, suchas the usual catch-sample from the surge tank 38 asindicated diagrammatically at 53.; Means are also provided for adding suitable correctionmaterials to the contents of the slurry mixers 43 and 44 as, indicatedat 54 and 55,-to effect any final correction necessary.

a In the operation of the system and apparatus,

shown in diagram in Fig. 1 to carry out the method of the invention, theraw materials, classified into two portions, one of high lime and one oflow lime content, for'example, the limestone and shale, or limestonewithlittle or no clay and limestone with more clay than that requiredfor 'a proper mix, and properly crushed for grinding, say aboutthree-fourths inch, are stored in the high lime and low lime supply bins1 and 2 respectively, ac=

cording to their lime content, and fed therefrom 1 through the feedregulating means 5 and 6 into swThe hOwl classifier 9 isarranged todischarge,

the primary mill 3 along with the necessary amount of water suppliedthrough conduit 11 to bring the contents of the mill to the optimumdilution or viscosity for grinding to the size de sired. The mill 3being arranged in closed cir-' cuit with the classifier 7, dischargesthe ground materials thereinto, water being added from the source 12 tobring-the dilution from that of the optimum grinding dilution to thefurther dilution desired for classification. The classifier operates toremove the oversize and return it to the mill 3 asindicated by fiow'line 57. From the classifier 7, the fines with the bulk of the water,-overflow into the bowl classifier 9, from which theintermediate oversizeis fed into a secondary or fine grinding mill 13 as indicated by flowline 58, which secondary mill, being in closed circuit with the bowlclassifier 9, delivers its discharge into the bowl 8 of the classifieras indicated by flow line 59. Where 'there'is insufiicient clay or itsequivalent in the raw material supplied from bins 1 and 2,

the required amount of clay may be added to the contents of the mill 13as indicated at 16. Water is supplied by 15 to the mill 13 to bring itscontents to the proper viscosity for efiic'ient grinding at the sizedetermined upon. Where the ma'-' terial supplied from the bins 1 and 2containsa considerable amount of natural fines, the feed therefrom maybe run directly into the classifier noes-gees than" three-fourths 'inchand more; suitable for skilled in the art;..; 1'

proper dilution 'for final classification water added'as indicated at1'4. At't his final and high est dilution the finished fines"overfiowing"thebdwl 8jarepassed into the annular feed-launder 2150f thethickener 17,flthe" mixture bei'ng maintained in sufiicient turbulenceand dispersio'non its way past the sampler 20- to-the' thickener to 5enable a substantially 'pe'rfect sample to be taken. Samples are thus'repeatedly taken and analyzed to ascertain thecoinposition of thethickener feed. The thickener feed passing"int o" thelaund'er 27 isdistributed thereby' into the thickener-17in the usual manner. a i 3 Therake arms 23-24r'otate at the proper speed-to rake the settled materialinto the cen-" tral discharge point 25 and produce a slight-dist'u'rbance as hereinafter described,butirisufiicient to preventthedesired decantation; The thick-""- aneu- (lisch'arge or underfiow passesonthrough the ii'nderflow line 26 to pump sv-rrom whence it is passed onthrough flow line 39 to thesurge tank 38;; rram" the surge tank theslurry is conducted on through flow line 40 to one of the-batchslu'r'rymixers; sayil a sample of the slurry being taken: at52.'"From the slurrymixers 41'-and"42"'the slurryisdrawn into the equalizing storage tank47', the batchmixers being alternately filled and drawn, one drawriwhile the other is being filled and its contents tested-and corrected tobring it to thefinal desired adjustment of complex ratios, such asratiosof iron, silica, alumina and soluble salts From theequalizing'tank 47 the" slurry is ruiieither directly to a kiln forburning or-"first througha filter and then to the kiln.

the'dilution of the discharge from the =secondarymill 13 is only thatnecessary ;for optimumgrind-ing, viscosity is relatively low and maybeas owasthat at which the final raw product is passed' to" thekilnfor'burning; jIt istherefOre necessary to further dilute thedischarge of mill- 13 for hydraulic classification in the bowl classiefler9;which dilution is effected as it isfed into thebowl 8 along withthe overflow fromclassifier 'l w'ith additional water supplied 'at jll'. Asthe an analysis of the composition of a sample, which time forexainple, may be in theneighborhoodof two to'four hours, and issufficient to give the operator a definite accounting of the average beeirig carriedin the thickener. This timeghowever,"

is srfian compared with the time 1 r detention in:

thethickener, whose equalizing effect-on anyva riati'on in compositionof feed is brought to a highgdegree of' perfection by rotatihgtherake;

armsat a speed sufficient to "properljrakejthe' thickened underflow tothe point of'discharge with slight stirring, insufiicientlto prevent theI desired decantation or settling, and by having the capacity or "thethickener so large in propo'r' tion tof -the; rate of feed andintervalsofanalysisand eorrectiong-that the quantities of mixture'fedinto" the thickener during suchsuccessive-periodsaresprea'din-"stratasuflicien'tlythintobe inter-- arms-v Thiscoordination of magnitudesof time; capacity of settlingz'one and rate ofstirring 'an important feature ofthe' invention whichmakesfor-theattainment of my objectofimproved con trol'of'thecomposition o'f-theproduct? P Tl1e?underfiow from the thickener thus of a compositionwh-ich is an "average of the total volume of mixture t ed into thethickener {foraim-1g period of-timerelative tothe time betweencorrections of such mixture, with the result thatany changein thecomposition of the uriderflow' takes the IOrmfof a gradual "trendrequiring along-time; in the neighborhood of several days,- to? exceed-apermissiblemarginf which makes the taking of ordinary catchQsamples at52* suflic'ient tof indi cate changes 2 in the trend in-timegtomake'suit--' able correctionin thickener-feed to offs'et a-trend towardexcess. Such offset'may be"accomplishedl by making a correctionover-compensating ifor the reduirementf indica'tedby the a'na'lysis ofthe catch sample w'hich accelerates the trend 1 anopposite directionsufiiciently to prevent the trend;

rr m exceeding th permissiblevariationg A5 a specific; practicalexample' offeed control; and thickener underfio'w response, an analysis{at intervalsoftwo to four hours gives the operator? definite knowledgeor what he is grinding and'a definiteaccounting of the average being"carried in the thickener. The raw mill leed for one pe==- riod isroughly adjusted tocompens'ate'fo'r dis-= crepancies of I the precedingperiod and the variations between 'the different periods are permittedto average outin the thickeneri Sh'ort ire-- riod variations inthe {mix going to' the 'thicken'er except they affectthe' averag'eofabout 36 hours operation. Even when a distinct'and -per manent changeis" suddenly made in the" nix' 'to the thiCkenelfl-the swing towardit ththickerler discharg isglfadfial. 1J1

In addition to the tendency to variation in dir ferent thin" strata;due' to slight variations 'i-n c'oinposition of feed for brief intervalsoftimeffor: making -correctionsaccording' to the requirements indicatedby analysis of f the samples of feed; which variations are substantially'ofiset by the= slight disturbin'g effect of the -rakei mechanism on therelatively thin strata,=there is aslight varration *incompositionat-fdifferent intermediate zones in the thickener due to differenceEh'IIQSBlT-i' tling rate of the different-main constituents sot thateven though -the' composition of the 'solidconstituents of feed, andconsequently the com-J position of the solid constituents: of i theundemflow are uniform; there will: be a 3 zone near .1 the top ofthe.thickener where the composition will; be low in lime, aniintermediatezoneiwherethe;

composition ;will be higherin lime. and -a zone near the discharge Wherethe compositionofthe thickened mixture will be that of the .feed.

n; be clear whenit is recalled that with an ev -Y n ior liquids only allthe solids in tile feed ill: pass out withthe underflow so that the co1% tion of the mixture of solids in theundeifiowwfll beident icalgwiththat ofvthemixtu'fe 6r solids in theifee d regardless of intermediatestra fication due to difie'renjc'e in settling" ate of differ n StituentSolids,"

f This intermediate segregation page of to bring" about a nner andrelativuy'more rapidly responsive control vofg-tlie composition ofv theunderflow without having to wait for a. change inthe trend iii-responseto anadjustment in feed;

by the practice of what'may be termed closed circult. thickening which;is. accomplished-through,

the. use of the, arrangement for recirculati'ng the underfiom; Tothis-end, aportion of the1-.under-- closed andathe valve 36, opened soas to direct.

the return from. surge tank.38 through flow line 49, valve-36 and pipe,3ltoa-zone in the thickener near the central pointI of :thickenerdischarge, whereby the-vcha-racteruof the discharge is un--. changedduetothe fact that in thiszone the, composition of. thematerialis the sameas that being returned.

. r If the under iiowiislow lime," then. valves 34, and 36 aremaintained closed andtvalveopened to; feed the return fromfeedqwellfillthrough valve- 35 and pipe 33' 1303.11 intermediate zoneqofrelative: 1y high lime; constituenhthus displacing the highlimemixturewithlow-limemixture with the result that .the movement of,the, displacedhigh lime mixture toward the discharge is hastened, while, at the sametime? the returned low-limemixture. is: placed a little nearer to'theincoming high-limecorrective feed. I 7 0n theotherha nd, if :theunderfiow is too. rich in lime, valves 35 and 36 are maintained closed.and valve 34 opened'to direct the return through Valve34 and pipe 3 2'toan upper zoneof low-lime mixture, thus displacing the lovv-limevmixture,

with a. high-lime mixture, with theresult that;

the movement of the displaced low lime mixturetoward the discharge is-hastened, and at the same timethe returned high-lime -mixture is;placedv H. near the incoming low-lime corrective feed, thus.

fastening, equalization. v

The numberof; return; feed; pipes; such as 31,, wand, 33, and-thelocation of the zones in the. thickener towhich-they distributethereturnfeed, may be ,variedaccording to the location of the;

different; zones of variation in. mixture, the shapeand proportions,of;the thickener, andthe: characteroi rawmaterialsgused.

From the surgetank 38, the; uncle is passed.

via flow lineg iogto. one of the batchslurrymixers, say 43, the.;valve41 .being opened and the valve 42.closed for this purpose. When desired,the slurry passingintotheslurry mixersmay besam pled'at some point;in-theflow line .as at. 52 instead of'or-in addition tothe catch samplestakenat'the'surgettank 38-: Final; correction for obtainingihe-finaldesired complex ratios,- iff necessary-{is accomplished in the slurrymixer byad'ditlon ot th'efproper amount and kinds of correc tion'materlals', as'indicated at '55'jin a man ner well understood by thoseskilled 'in-the art. After theslurry 'mixer 43 is' filled, the-valve 41is cioseaana" t e "valve 515 opene to reed the con-- tents of the mixerto the fequalizing storage tank 47, while the supply of slurry from thesurge tank is diverted to,th e nextislurry mixerffiji'andso on accordingto the number of 'slurry'ffniixers. used.

From the storage tank 47 the mixture 'i'sflfed" ihi l -fi9 l i afii itin ?ihew directly-or} first through; a: suitablefilter brother"suitable further dewatering-device.;-. M

The-long. period of settling in the thickener: the: substantial storageof settled slurrythat is carried above the discharge point; in'thethickener gives a discharge moisture that is substantially free fromvariation as long as the averagesettling: character of. the rawmaterials remains oonstant..-; Where the settling character of, the rawmaterials changes, the swing of moisture in. the thickener; discharge isvery gradual .per mitting reliable readjustment of slurry-feeders orfilters aheadof the kiln-so that constant,ton-- nage rates through thekiln can be maintained. Evenii the feeders or nlters'are notreadiusted.the; change: is 0 gradual that conditions of ir.-. regular depth ofcharge different parts of thekiln atthe same time are avoided and auniformly burned clinker can. be obtained..-

It will be understood that the system-or plant and its operation asabove described is not-dependent on the; specific elementary components:falling strictly within the definitions used,i n-., thedescriptionforthe sake of disclosure,;-f0r example, the term flow line is .,used toindicate any known or other suitable form of means or; arrangement forconducting, guiding or convey-5 ing material from one point to another,,such as a pipe, trough, conveyor, et c according to the, nature of; thematerial conveyed andother ex igencies of the particular phasein theprocess. Also the term valve is used to indicate any known or othersuitable means for controlling the. flow of material such as any knownform of valve,

. stopper, gate or the equivalent selected according to the kind ofconductor or conveyer-in which it; is. used and the nature of thematerial whose flow is to be controlled. 3

The above described system of composition control is in practicesubstantially a one pointcontrol system, because the sampling andcontrol of the thickener feed. islthe. only oneeessential outside of theoccasional.checkingotthe trend of underflowcomposition and its. correction locally by, manipulation oithe recirculation through the thickenerpending response to control of thethickener f eed. I Referring .now toFig. 2, this shows a modifi cation using two relatively smallequalizingstorage thickeners'lqand 'Zl instead of a single relativelylarge thickener- The grinding is here shown, as of the single stagetype; but itis to be understood that it may alsobe of the double:stagetypeas shown in Fig l, Here the raw materials are stored inhigh-lime and low-lime bins 72 and. 73 respectively, according to their.composition, which bins are arranged to supply the. materialsv in propercontrolled ratio, over-Qflow line '74 to the mill .75., A Dorrbowl-classifier 76 is. arranged. in closed circuit with the mill 75-through iiow lines 77 and78, withits overflow discharging through flowline 79 to the equalize ing storage. thickeners '70- 7l, ,an automaticsampler 80 of anyknown or other suitable type; being operativelyassociated ,with the .ifiow line 79 for taking composite samplestherefrom. The; flow line 79 feeds the thickeners through branch.-lines- 31 and 82 provided with suitable valve eIements 83 and 84.Overflow from the thickeners is eturned to the bowl classifier overflowline 85.. Underflowfromthickeners 70 and 71 is conduct ed over suitableflow lines 86and 87. respectively, to. several (small, preferably 8-hourcorrection, tanks 88,. 89- and'90, selective distribution to the tanksbeing effected through branch conduits 91,,

92,%."8t0.;f controlledby valve elements .97, 98,1etc.

1 Go'nduitsw 103 a I etc., provided with: suitable "valve i urIntcarrying out' the method with the system just described" above,thebowl classifier overflow is'divert'ed from fiowlline '79 overflowlimellthickenerwl, respectively, according asto whether the analysesoftthe samples taken at80 indicate the overflow to 'be of -high lime Icontent on low lime' -content- The thickened slurry is drawn: from boththickeners '70 and '71 intoxthe correction tanks 88"etcJ, to fill themwith mixture of the desired composition, which composition-is controlledby proper 'propo'rtioning of the mixturesf furnished by the difierent',thickeners' in accordance=with'thef lime content of suchmixtures shown1 -by analyses of l the samples" taken at 11 1 and 1 12 1 Advantage is"taken of the in'-- herent i equalizing efie'ct of the; thickeners" toinsure" against substantial change in composttion of thioken'er'under-flow in the time interval between the samplinghand analyzingy withthe result that a very fine control of the-composition of the Inixtureinthe correction tanks is accomplished.

From the correction tanks the slurry is passed to the usual equalizingstorage 109 from whence it is fed as required over fiow line 110 tosuitable kilns not shown. To enhance the equalizing effect of thethickeners they may be operated periodically as slurry mixers by drivingthe rakes at relatively higher speed, preferably so operating one whenthe other is receiving all or substantially all of the feed. I

Where the high-lime and low-lime thickeners are of a size suificientonly to handle a portion of total feed from the bowl classifieroverflow,

for example 75 per cent, the arrangement of Fig.

3 is used, wherein the overflow, after passing thesampler is caused toflow through a suitable splitter 125 to split the feed to the thickenersin the ratio of 25 per cent to the low-lime thickener '71 and '75 percent to the high-lime thickener 70, when the analyses of the samplesindicates a high lime content, and in the opposite ratio when theanalysis indicates a low lime content.

Where it is desired to use a still larger number of smaller thickeners,say three, each of a capacity sufficient only to handle say 50 per centof the total overflow from the bowl classifier, the

' arrangement shown in Fig. 4 is used wherein the the high-limethickener '70 and a tertiary or.

medium-mixture thickener 132, the splitter being arranged to dividethefeed equally between the two thickeners. The fiow line 127 is similarlyarranged to conduct the feed through a suitable splitter I31 intet1ualsproportions r to the low lime valve element129 is closedlandthelvalveelement a 128 opened to divert; the feed overflow: line .126 and throughsplitter 130. inaequakproportions to the thickeners and .132. .1Likewise, when the analyses indicate: a 10w: lime content 1 valve ele'-"mew-.2128 is 1 closed? and: 129 opened to divert the feed through: flowline? 127 and splitter 131,. in equal proportionstothickenerss'fll:andxl32. '1aThe three thickeners will thus serve'as-equaliz-' ing storage zones for the :mixtures of three differentcharacters,=' highivlinie, :1 low "lime! and medium; lfrom l which the'f-underfiow may be drawn sin'properiiproportions for mixtures in theusual suitable tcorrecticn:,;=tanks,- in a mannerwhich will be wellunderstood in the light ofthe description of Figa 23 2: J Itwillfbeclear fromther above that-thisphaSe of the inventioninvolvingthe' splitting" ofthe feeduinl different prop'ortionstodifferent thickeners will be waried in its application according to thecapacity of the 11 thick'eriers' in relation to the .volume of=feedsupply. For example; where three thickenersare used each of 'acapacity less than 50 per centof -the total supply,- a threeway splitterwould be used, arranged'to divide as much of the feed as can be handled.by two thickeners; equally between one i of 1 the extreme thickeners andthe tertiary-thickener;diverting the small remainder t'os the" otherextreme thickenen the distribution bein'g alternated in relation to theextreme thickeners according to variations in the lime content ofthefeedl A -modification of this latter system of feed is to feed one ofthe extreme ,thickeners at full capacity (less than half the totalsupply) and distribute the remainder of the supply equally between thetwo remaining thickeners.

While certain specific modifications, embodiments and. applications ofthe invention have been herein shown and described for the purpose ofdisclosure, it is to be understood that the invention is not limited tosuch specific embodiments and applications, but contemplates all suchmodifications and variants thereof as fall fairly within the scope ofthe appended claims.

Having thus described the invention what is claimed and desired to besecured by Letters Patent is:

1. In the process of manufacturing cement by wet grinding, the method ofcontrolling the composition of the finished ground mixture to be burned,which comprises passing the finished groundmaterial into a settlingzone, withdrawing a portion of the settled mixture for said burning,analyzing a sample of the portion withdrawn for burning, and returningto the settling zone a portion of the mixture withdrawn, to displace aportion of the mixture in the settling zone having an excess of theelement needed in the sample tested.

2. In the process of manufacturing cement by wet grinding, the method oicontrolling the composition of the finished ground mixture to be burned,which comprises passing the finished ground mixture into a settlingzone, withdrawing a portion of the settled mixture for saidburning,analyzing a sample of the portion withdrawn for burning, and using aportion of the mixture withdrawn to displace portions of those strata inthe settling zone containing a corrective mixture and therebyaccelerating-Lthei movement the displaced portion towardthepointof-discharge.z 7 i 1 35: In a process; of; manufacturing cementincludingasteprat which theiground raw mixture offlgive'n desiredcomposition is detained in relativelylarge :volume, and portions thereofwith-.

drawn:- from the zone "of? detention; the method of; varying thecomposition of the mixture withdrawnf-rom: the zone of 1- detentionwhich comprises displacing portions." of v the .mixture in the zone of:detentiomhavingan excess; of .the element .wanting in: i the -mixturewithdrawn with pontion-of'theemixture Withdrawn to disturbthestratification of portions ofdifierent composition int-the zone.of.:detention.; 1 y :-iEn.,:a process of manufacturing, cementincluding a stepiati whichithe' ground raw mixture of given desiredicomposition is:;detainecl in relatively; large volume, rand portions,thereof with? drawn from the zone of detention; the method of :controlling theqcomposition withdrawn from the zone;;of detention whichcomprises using a portion of-;:the;- mixture withdrawn tofldisplaceportions of those-strata containing a corrective vmixture-and therebyaccelerate the movement of such portions-toward .the'point of discharge.115, -';I'he.process,of;makingcement which comprises segregating-.thelraw material into highlime-randlow limezsupplies, proportioning amixtureof the said supplies to form a grinding mill feed;= r.injdingthermill feed, hydraulically classitying the; mill discharge-passing theclassifier v overflovw; to,; ai thickener, sampling 1 and analyzing theclassifier,overfiow sampling: the thickener discharge, varying the saidmixture of, raw materials tovary the composition of the classifieroverflow as indicated by the hanalysis-of such overflow to compensate.for variation 'inathe thickener discharge as indicated by the analysisthereof, and accelerating the movement of oer-1 tain high-lime orlow-lime portions of the thickener contents toward the discharge: tocorrect composition of discharge during time required to effectcorrection of thickener contents by variation of raw materialcomposition, byvretumingor recirculating thickener underfiow to ,certainsludge zones in the thickener in a manner Sub-Q stantially as described.1'

6. In the manufacture of cement by wet grinding, the method ofcontrolling the composition'of theJfinished ground mixture to be burned,whichcomprises passing the finished ground mixture into a 'settling zoneat a dilution greater-than that of the mill discharge, repeatedlydiverting :a' portion of the feed in its passage to the settling zoneand analyzing said sample, varying the composition of the feed tocompensate foreany variation from the desired composition as indicated'bysuch analyses, withdrawing the settled mixture; from thesettling zone for burning, sampling and analyzing the mixture withdrawn,and controlling the composition of the mixture withdrawn to compensatefor fluctuationsin the. composition of the feed by'returning to theysets tling zone a portion of the'mixture withdrawn to displace otherportions of the mixture in the settling zone such as are rich in theelement wanting in, the mixture withdrawn to accelerate the movement ofsuch displaced portions tothe point of discharge.

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